Pacta conventa (Latin for "articles of agreement") was a contractual agreement, from 1573 to 1764 entered into between the "Polish nation" (i.e., the szlachta (nobility) of the Polish–Lithuanian Commonwealth) and a newly elected king upon his "free election" (wolna elekcja) to the throne.^[1][2]

The document was drawn up by the convocation sejm.^[3] The pacta conventa affirmed the king-elect's pledge to respect the laws of the Commonwealth and specified his undertakings and promises in such realms as foreign policy, taxes, public debt, the military, and so on.^[2] They varied from king to king, depending on whatever particular pledges he might have made.^[2] An example of the various concrete undertakings found in a king-elect's pacta conventa is King Władysław IV Vasa's pledge to create a Polish–Lithuanian Commonwealth Navy for the Baltic Sea.

In addition to his own unique pacta conventa, each king-elect was required to sign the Henrician Articles, a set of privileges named after the first king who signed them, Henry of Poland.^[2] Unlike the pacta conventa, the Henrician Articles were constant and unchanging.^[2] The distinction between the two documents gradually faded away over successive elections. Together, those two documents spelled out most of the critical details of the Commonwealth political system.^[2]